Method of producing graphitic carbon



l. H. DERBY Oct. 2, 1934.

METHOD OF PRODUCING GRAPHITIC CARBON FiledA April 27, 1929 III-II m1# Patented @et 2, i934 Fria METHOD F PRODUCING GRAPHITIC CARBON lll-a H. Derby, Indianapolis, llnd., assignor to Peter C. Reilly, Indianapolis, Ind.

Application April 27, 1929, Serial No. '358,553

Claims.

This invention relates to a process for the production of graphitic carbon and the resulting product.

The process is preferably a continuous one. A

5 suitable starting material is a pitch coke from coal tar or petroleum, preferably the coke described and claimed in U. S. Letters Patent to Reilly, 1,230,782, whether produced by the process of that patent or otherwise. Other similar starting materials may be used.

Generally stated, the starting material is heated partly by surface combustion and partly by external means, preferably electrical. Commonly there are two heating zones, the rst a combustion heating zone and the second the electrical heating zone.v ,'I'hese, for economy, are closely juxtaposed and may even overlap more or less, so that combustion continues in the electrical heating zone. The process is preferably carried out in a vertical furnace or retort in which the charge descends'. The charge approachingv the combustion zone moves in counter-current to the products of combustion so as -to be heated thereby. The products of combustion are drawn off by suction so that the process takes place under sub-atmospheric pressure. The maximum temperature is about 2500 C. and except under special conditions should not exceed 2900 C. for good economic effect. The finished product after $0 leaving the high temperature zone.` is protected from air currents so lfar as practicable.

' While the process may be carriedout in various types of apparatus, it will now be described, for purpose of explanation, as carried out continuously in a vertical furnace illustrated in some detail in the drawing.

In the drawing,- y

Fig. 1 is a vertical axial section of the furnace.

Fig. 2 is an enlarged sectional View similar to a portion of Fig. 1, showing rthe electrically heated portion of the furnace.

Fig. 3 is a section on the line 3-3 of Fig. 2.

Fig. 4 is a section on the line 4 4 of Fig. 2.

Fig. 5 is a fragmentary view similar to Fig. 2,

showing a modification.

The furnace shaft or retort is built of any sultable refractory and is about thirty feet high.

The retort proper, 11, is preferably of a attened, approximately elliptical cross section, as

shown, for thereason that the penetration of air or other combustion-supporting gas entering by the tuyres `12 is essential and will'foccur only through a layer of material of a limited thickness.

This thickness varies but ordinarily is from 8l to 12 inches depending on the size and character of the material.' A circular furnace would necessarily be of a small diameter, say not over twentyfour inches, and consequently of small capacity. The desired capacity is secured by enlarging only .o one transverse dimension, so'that the material be- .circulating water or other cooling fluid through ing treated flows in a stream of any desired width, but of a thickness so limited as to ensure penetration of the combustion-supporting gas throughout the stream of material.

In the embodiment shown'the tuyres 12 lead directly from the atmosphere as the furnace is designed to be operated at sub-atmospheric pressure, and the combustion-supporting gas is air. It has not been found necessary to heat this air, but such treatment is known and falls within the broad scope of the invention. Changes in details are possible but the illustrated arrangement operates satisfactorily.

The offtakes 13 lead from points near the top of shaft 11 to an exhauster of any suitable type (not shown), which withdraws the products of combustion and maintains the retort at the desired sub-atmospheric pressure. 'Ihe withdrawn products of combustion are a good grade of producer gas and may be usefully applied by methods known in the art. f

The feed hopper 14 is provided with a top gatevalve 15 through which it is charged and a bottom gate valve 16 through which it discharges into the retort 11. Only-one valve is opened at a time so as to preserve the isolation of the top of the retort from the atmosphere.

Immediately below the zone of the tuyres 12, as shown in Figs. 1-4, or approximately coincident therewith, as shown in Fig. 5, is the electric heating zone. This has a graphite lining made up of one or more conducting, heat resisting graphite annuli 17, which collectively serve as the heating elements and constitute the secondary circuit of the inductlonfurnace. The primary is a Imassive tubular copper coil 18. The convolutions of the primary coil 18 are supported and electrically insulated by specially formed refractory blocks 19. The space intervening between the blocks 19 and the annuli 17 is filled with lampblack, powdered graphite or other, suitable material, 21, either in powdered form or compacted into blocks.

The electric heating devices chosen for illustration will be recognized as an adaptation of the Ajax-Northrop type of induction furnace.

The induced current in the secondary with its resistance effect,develo s the desired heat.

.The coil 18 is protec ed'from overheating by the tubular coil. The ow is controlled by valves no 22.V

The retort 11,0pens into aclosed chamber 23, below it, in which the heated material is held while cooling, and from which it is discharged without permiaingthe admission of air. `The discharge isv effected by a screw-conveyor 24 to a- -spout 25 having a valve 26. In practice the valve 26 is opened merely whengthe spout 25 is connected air tight, or substantially so, to a. closed Container (not shown is considered im- 120 portant to prevent the access of air to the finished material cooling in chamber 23 and any means to eifect this end while discharging finished material will serve. Manholes are shown at 27.

Using pitch coke, preferably of the type specied, as the startingv material, ignition in the retort 11 is eifected in any suitable manner. The operation will ultimately become stabilized about as follows, it being understood that the first product may require to be retreated or discarded.

The gaseous combustion products are withdrawn by the exhauster through the offtakes 13 at a temperature of about 150 C. The suction at the top of the retort is equivalent to from 25 to 50 inches of water. The suction at the tuyres is equivalent to about 11/2 inches of water. The descending charge rises in temperature some 160 C. per foot of descent until it reaches the combustion zone. The rise of temperature in the lower portions of the furnace is more rapid. Decomposition of the carbon components constituting the charge begins between 350 and 450 C. according to the nature of such compounds.

In the form of Figs. 1-4 the material reaches in its approach and passage through the tuyre zone a temperature of 1600o to 1800 C. and undergoes a chemical change to a product intermediate the original coke and the final graphitic product. Down to this point the heat is generated by surface combustion of the material, and with the methods shown, 1800 C. is about the limit attainable without undue carbon consumption.

'Ihe further descent through the electrical heating zone is accompanied by heating to about 2500 C. though temperatures of the order of 2900 C. have been used. The effect is to drive off any remaining hydrogen and ash material and convert the intermediate product above-mentioned, and not here claimed, into almost pure graphite in the form of large unctious lumps having a cellular (bubble-filled) texture. The current used in the primary is a high voltage high frequency alternating current. Voltages of seven to eight thousand have been successfully used, for

example.

In the form shown in Fig. 5 the tuyre zone coincides approximately with, or at any rate overlaps, the electrical heating zone. 'Ihis implies subjecting the material to rapid oxidation and the high heat developed by electrical heating simultaneously. This is technically possible but accelerates the consumption of carbon as an offset to its apparent advantage in conserving heat by reducing the total surface through which heat is radiated from the furnace. While the economic factors have not yet been accurately determined, it is believed that arrangements having at least some overlap of the tuyre and electrical heating -zones will prove commercially desirable. 60

From a chemical standpoint the two arrange-i ments appear to be substantial equivalents as the final products are essentially similar.

In either case the material leaving the electrical heating zone passes slowly down through the chamber 23, gradually giving up its heat, while protected from substantial further oxidation.

The resulting product has a purity of at least 99.84% whereas the starting material is only about 90% carbon. The product is soft and friable and of high electrical conductivity. The structure is cellular or honeyombed, and not flaky. The. material can readily be reduced t0 powder and is lacking in any abrasive property.

The density of the nal product varies from about 2.20 to about 2.25, depending on the length and intensity of heating. The differences in density are apparently dependent on the degree of graphitization. Regardless of the slight variation in density noted, the electrical conductivity appears constant and equal to that of pure graphite. The ash content decreases as the temperature of final treatment increases, indicating that certain ash-forming constituents are volatilized or consumed at or near the upper temperature limits.

What is claimed isz- 1. 'I'he method of producing graphitic carbon, which consists in passing a coke selected from the herein described group consisting of coal tar coke and petroleum coke to and through a heating zone in which the coke is progressively heated by surface combustion in an atmosphere containing oxygen at sub-atmospheric pressure until a temperature of the order of 1800 C. is reached, and then through a zone in which it is heated by external coreless electrical induction furnace means to a temperature of the order of 2500 C.

2. The method of producing graphitic carbon, which consists in passing coke to and through a heating zone in which the coke is progressively heated by surface combustion in an atmosphere containing oxygen until a temperature of the order of 1800 C. is reached and then through a zone comprising a coreless induction furnace in which it is heated by electrical induction to a temperature of the order of 2500 C.

3. The method of producing graphitic carbon.

which consists in passing a coke selected from the herein described group consisting of coal taxl coke and petroleum coke to and through a heating zone in which the coke is progressively heated by surface combustion in an atmosphere containing oxygen untila temperature of the order of 1800 C. is reached and then through a .zone comprising a coreless induction furnace in which it is heated by electrical induction to a temperature of the order of 2500 C.; withdrawing the heated material from the second heating zone and passing it through a cooling duct in which it is protected from the access of air; and passing products of combustion of the first heating zone in countercurrent with the entering coke.

4. The method of producing graphitic carbon, which consists in subjecting a coke selected from the herein described group consisting of coal tar coke and petroleum coke to a progressively increasing temperature in a current of oxygen-containing gas and until a temperature of the order of 1800 C. is reached, the heat being furnished by combustion; and adding heat by means of a coreless induction furnace until a temperature of the order of 2500 C. is reached.

5. That method of producing graphltic carbon which consists in subjecting to a temperature of the order of 2500 C., coke selected from the herein described group,A consisting of coal tar or petroleum coke, in a coreless electrical induction furnace having a refractory electrically conducting lining in which current is induced and from which heat is radiated into the charge. 

